the long way to do it is to say that your 2013 pts are valid for stays from 8/1/13 to 7/31/14.
if you borrow them, they become valid for stays from 8/1/12 to 7/31/13. (and remember that banked and borrowed pts can never be put back in their original use year.)
so you could have called as early as 9/1/11 to book 8/1/12 using borrowed 2013 pts...